1. Field of the Invention
The present invention relates to a single pass type color image forming apparatus, and more particularly to a color image forming apparatus capable of supplying power to a plurality of developing devices, transfer devices and charging devices with a single power supply device.
2. Description of the Related Art
Generally, for a high speed image formation, a single pass type color image forming apparatus is provided with a plurality of color image forming units which are arranged along the traveling direction of the transfer belt to form a color image. Such a single pass type color image forming apparatus is sometimes called a tandem type color image forming apparatus. The plurality of color image forming units generally represent cyan (C), magenta (M), yellow (Y) and black (K) color images. The color image forming apparatus may be, for example, a color printer or a color photocopier that can reproduce color image on the printing medium.
FIG. 1 shows a conventional single pass type color image forming apparatus.
Referring to FIG. 1, the color image forming apparatus includes a plurality of color image forming units, a transfer belt 50, a paper transfer unit 40 and a plurality of power supply units.
The plurality of color image forming units are arranged along the traveling direction (arrow) of the transfer belt 50 for forming cyan (C), magenta (M), yellow (Y) and black (K) images. The color image forming units respectively includes photosensitive bodies 10C, 10M, 10Y, 10K for transcribing the image onto the transfer belt 50, transfer units 30C, 30M, 30Y, 30K arranged opposite to the photosensitive bodies 10C, 10M, 10Y, 10K with respect to the transfer belt 50 disposed therebetween, and developing units 20C, 20M, 20Y, 20K for developing an electrostatic latent image formed on the photosensitive bodies 10C, 10M, 10Y, 10K with a developer such as toner or ink. On one side of each photosensitive body 10C, 10M, 10Y, 10K is formed charging unit 12C, 12M, 12Y, 12K for charging the surface of the photosensitive body 10C, 10M, 10Y, 10K, and on one side of each developing roller 21C, 21M, 21Y, 21K is formed a feeding roller 22C, 22M, 22Y, 22K for feeding a developer to the developing roller 21C, 21M, 21Y, 21K.
An image of respective colors is formed on the transfer belt 50 by the plurality of color image forming units as the respective color image are sequentially formed on one another, and the complete image is transcribed by the paper transfer apparatus 40.
The paper transfer apparatus 40 transcribes the color image from the transfer belt 50 onto a printing medium 49 fed from a printing medium feeding unit (not sown) and then fixes the image.
A power supply apparatus supplies power to the respective units and includes separate power supply units that supply power to each of the units. Accordingly, provided to the power supply apparatus are: a plurality of first power supply units 24C, 24M, 24Y, 24K, 23C, 23M, 23Y, 23K, 14C, 14M, 14Y, 14K for supplying power to the developing rollers 21C, 21M, 21Y, 21K, feeding rollers 22C, 22M, 22Y, 22K and charging rollers 12C, 12M, 12Y, 12K; second power supply units 32C, 32M, 32Y, 32K for supplying power to the plurality of transfer rollers 30C, 30M, 30Y, 30K; and a third power supply unit 46 for supplying power to the paper transfer apparatus 40. In other words, at least 16 separate power supply units are required. Each of the power supply units supplies a different voltage level suitable for the corresponding process performed by the unit to which it is associated, and the level of the voltage is adjustable with respect to each of the power supply units.
As described above, in a conventional single pass type color image forming apparatus, since separate power supply units are respectively required for each of the rollers and transfer rollers of the color image forming unit, the size of the color image forming apparatus tends to be large and costly to manufacture. As a result, there has been a demand for a simplified color image forming apparatus with a simplified power supply unit, tending to be smaller and less costly to manufacture.